<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        #app1{
            margin-top: 200px;
            width: 300px;
            height: 400px;
            border: 1px solid red;
            /*margin-bottom: 100px;*/
        }
        #app2{
            width: 200px;
            height: 200px;
            background-color: green;
            /*margin-top: 200px;*/
        }
    </style>
</head>
<body>

<div id="app1">
    <div id="app2"></div>
</div>

</body>
</html>